It is required in a glass manufacturing apparatus such as a vacuum degassing apparatus that a constituent material of a conduit for molten glass is excellent in heat resistance and corrosion resistance to molten glass. Platinum or a platinum alloy is used as a material satisfying the requirement (Patent Document 1). An insulating brick is arranged around a conduit for molten glass made of platinum or a platinum alloy so as to surround the conduit.
The platinum or platinum alloy constituting the conduit, and the insulating brick arranged around the conduit have different coefficient of thermal expansion. Therefore, the difference in the amount of thermal expansion when heating and the difference in the amount of shrinkage when cooling become the problem.
To absorb the difference in the amount of thermal expansion when heating or the difference in the amount of shrinkage when cooling, unshaped ceramic material such as castable cement is filled between the conduit and the insulating brick so that those can slightly move relatively when the temperature change has occurred.
The present inventors have found that the filling with unshaped ceramic material may not absorb the difference in the amount of thermal expansion when heating or the difference in the amount of shrinkage when cooling, depending on the arrangement of the conduit for molten glass. For example, the difference in the amount of thermal expansion when heating or the difference in the amount of shrinkage when cooling cannot be absorbed by unshaped ceramic material at the junction between a vertical pipe and a horizontal pipe, and cracks are likely to occur at the junction. If cracks occur at the junction, there is a problem that an insulating brick arranged around the conduit is corroded by molten glass leaked from the cracks. This gives rise to the problems such that productivity is decreased due to repair work and the life of facilities is shortened.
To solve those problems, the present inventors have provided a molten glass conveying equipment element and a glass manufacturing apparatus, described in Patent Document 2.
In the molten glass conveying equipment element described in Patent Document 2, a ceramic structure having a coefficient of linear thermal expansion substantially equal to that of platinum or a platinum alloy constituting a conduit for molten glass made of platinum or a platinum alloy is arranged around the conduit, and thus, the difference in the amount of thermal expansion when heating or the difference in the amount of shrinkage when cooling become considerably small. As a result, cracks at the junction between a vertical pipe and a horizontal pipe due to thermal expansion when heating or shrinkage when cooling is prevented from occurring.